compiler/stdc/math/s_nexttoward.c

   1 /* @(#)s_nextafter.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_nexttoward.c,v 1.3 2011/02/10 07:38:13 das Exp $";
  15 #endif
  16
  17 /*
  18  * We assume that a long double has a 15-bit exponent.  On systems
  19  * where long double is the same as double, nexttoward() is an alias
  20  * for nextafter(), so we don't use this routine.
  21  */
  22
  23 #include <float.h>
  24
  25 #include "fpmath.h"
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 #if LDBL_MAX_EXP != 0x4000
  30 #error "Unsupported long double format"
  31 #endif
  32
  33 double
  34 nexttoward(double x, long double y)
  35 {
  36         union IEEEl2bits uy;
  37         volatile double t;
  38         int32_t hx,ix;
  39         uint32_t lx;
  40
  41         EXTRACT_WORDS(hx,lx,x);
  42         ix = hx&0x7fffffff;             /* |x| */
  43         uy.e = y;
  44
  45         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||
  46             (uy.bits.exp == 0x7fff &&
  47              ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0))
  48            return x+y;  /* x or y is nan */
  49         if(x==y) return (double)y;              /* x=y, return y */
  50         if(x==0.0) {
  51             INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */
  52             t = x*x;
  53             if(t==x) return t; else return x;   /* raise underflow flag */
  54         }
  55         if(hx>0.0 ^ x < y) {                    /* x -= ulp */
  56             if(lx==0) hx -= 1;
  57             lx -= 1;
  58         } else {                                /* x += ulp */
  59             lx += 1;
  60             if(lx==0) hx += 1;
  61         }
  62         ix = hx&0x7ff00000;
  63         if(ix>=0x7ff00000) return x+x;  /* overflow  */
  64         if(ix<0x00100000) {             /* underflow */
  65             t = x*x;
  66             if(t!=x) {          /* raise underflow flag */
  67                 INSERT_WORDS(x,hx,lx);
  68                 return x;
  69             }
  70         }
  71         INSERT_WORDS(x,hx,lx);
  72         return x;
  73 }